HSP90a plays an important role in regulating enzymes important for metabolic functions such as eNOS and LKB1. Therefore, it is possible that HSP90a plays a broader role in the regulation of energy metabolism in whole animals. To examine this possibility, we fed wild-type and HSP90a knockout mice with medium fat diet and measured body weight. We found that HSP90a mice accumulate fat faster than wild type mice. They also have less physical endurance in treadmill running. We will further analyze mitochondrial function in HSP90a knockout mice.